Polycarbonates are generally produced by using raw materials derived from oil resources. However, it has recently been worried about the depletion of oil resources and desired to provide polycarbonates from raw materials obtained from biomass resources such as plants.
Heretofore, studies have been made to obtain polycarbonates through transesterification with diphenyl carbonate by using isosorbide as a plant-derived monomer (for example, Non-patent Document 1, Non-patent Document 2 and Non-patent Document 3). However, since a homopolycarbonate obtained from isosorbide has a rigid structure, its glass transition temperature and melt viscosity are extremely high, thereby making it difficult to mold it. Since the thermal decomposition temperature of the isosorbide skeleton is low, when extrusion and molding are carried out at a temperature of 250° C. or higher, there occur problems such as coloration and the production of a silver streak. Further, as isosorbide has high hygroscopic nature, a polycarbonate polymerized from isosorbide also has high hygroscopic nature, thereby causing a problem such as a dimensional change by water absorption when it is used for application in molded articles.
As studies on the improvement of moldability, attempts have been made to copolymerize isosorbide with an aliphatic diol (Patent Document 1). In Examples of Patent Document 1, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol are enumerated as examples of the aliphatic diol as a comonomer. Moldability is greatly improved by introducing the aliphatic diol as a soft structure to provide flowability. However, there is a trade-off relationship between the aliphatic diol and isosorbide, that is, when the amount of the aliphatic diol to be introduced is large, heat resistance degrades whereas when the amount of the aliphatic diol to be introduced is small, the great influence of the isosorbide skeleton appears and water absorption becomes high.
Meanwhile, it has been reported that a polycarbonate having good balance between rigidity and toughness is provided by copolymerizing a bisphenol with isosorbide (Patent Document 2). In Examples of Patent Document 2, bisphenol A is studied as the bisphenol which is a comonomer. This two-component-based polycarbonate which comprises isosorbide and the bisphenol has high melt viscosity like a homopolycarbonate of isosorbide, and an extrusion/molding step at a temperature of 250° C. or higher is required. Therefore, it is difficult to use the above polycarbonate for application in a transparent molded article due to coloration and the production of a silver streak.
Studies have been made on the copolymerization of isosorbide with an alicyclic diol as another comonomer. In Examples, cyclohexane dimethanol and tricyclodecane dimethanol are enumerated as examples of the alicyclic diol. Even when these alicyclic diols are copolymerized, the obtained copolycarbonates are still unsatisfactory because they do not have high heat resistance and low water absorption at the same time like a polycarbonate obtained by copolymerizing an aliphatic diol (Patent Document 3).
Meanwhile, a terpolycarbonate obtained by terpolymerizing 9,9-bis(4-hydroxy-3-methylphenyl)fluorene (biscresol fluorene, BCF), isosorbide and an aliphatic diol or an alicyclic diol has been studied for use in films (Patent Document 4). However, the composition ratio and comonomers of the terpolycarbonate suitable for use in molded articles are not disclosed. Further, an effect obtained by controlling the terminal ratio is not disclosed at all. Although there is no problem when it is used for films, the terpolycarbonate obtained by Patent Document 4 is colored due to BCF. Therefore, it is desired to select comonomers suitable for use in thick transparent molded articles.    (Patent Document 1) WO2004/111106    (Patent Document 2) JP-A 2010-37551    (Patent Document 3) JP-A 2008-24919    (Patent Document 4) WO2006/041190    (Non-patent Document 1) “Journal fuer praktische Chemie” vol. 334, p. 298-3101, 1992    (Non-patent Document 2) “Macromolecules”, vol. 29, p. 8077-8082, 1996    (Non-patent Document 3) “Journal of Applied Polymer Science”, vol. 86, p. 872-880, 2002